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Re: Referencing elements of array expressions [message #3513]

Mon, 06 February 1995 08:18

velt
Messages: 19
Registered: June 1994

Junior Member

In article <3guag9$nqn@marsupial.jpl.nasa.gov>, "Evan F. Fishbein" <eff@tugh.jpl.nasa.gov> writes:
> A simple question -- Is is possible to reference elements
> of array expressions. For example, can the last two lines of
> the following code:
>
> x=findgen(40)/10.0
> y=cos(2.0*!pi*x)
> i=where(abs(y) lt 1.0e-5)
> i=i(0:1)+[-1,1]
>
> be combined into one line by accessing the first
> element of the expression "where(abs(y) lt 1.0e-5)"
> without placing the vector result in a dumy array variable?

This is a simple trick-question, isn't it? The where finds no elements
satisfying the condition, so the last statement will generate an error.

However, in general you can index expressions by surrounding it
with parentheses and indexing that:

IDL> result = (expression) (elements)

For example, the last two lines above can be written:

IDL> i=( where(abs(y) lt 1.0E-5) ) (0:1) + [-1,1]

Robert Velthuizen (velt@rad.usf.edu),
Digital Medical Imaging Program of the
H. Lee Moffitt Cancer Center and Research Institute at the
University of South Florida, Tampa FL 33612.

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[Message index]

		Re: Referencing elements of array expressions By: velt on Mon, 06 February 1995 08:18
		Re: Referencing elements of array expressions By: steinhh on Sun, 05 February 1995 18:10

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